 D0*D00(k)|MX(3872)-ED0*(k)-ED0(k)|2+14D0*2,


where \(\mathcal {M}^{JL}(X(3872)\rightarrow D^0\bar{D}^{0*})\)  is the \(^3P_0\)  amplitude defined in Eq.(REF ),
\(\Gamma _{\bar{D}^{0*}\rightarrow \bar{D}^{0}\pi ^{0}}(k)\)  is the energy-dependent
decay width of the unstable meson \(\bar{D}^{*0}\)  worked out within the chiral quark model [1]},
and \(\Gamma _{\bar{D}^{*0}}\)  is the total decay width of \(\bar{D}^{*0}\) . According to PDG, we have \(\Gamma _{\bar{D}^{*0}}=\Gamma _{\bar{D}^{0*}\rightarrow \bar{D}^{0}\pi ^{0}}/0.65\)  [2]}.
As the unstable meson \(D^{*0}\)  can slightly off shell, its momentum \(k\)  can range from 0 to
\(k_{max}=\frac{\sqrt{M_{X(3872)}^2-(M_{\bar{D}^0}+M_{\pi ^0}+M_{D^0})^2}\sqrt{M_{X(3872)}^{2}-(M_{\bar{D}^{0}}+M_{\pi ^{0}}-M_{D^{0}})^{2}}}{2M_{X(3872)}} \) . Using Eq.(REF ), we plot the decay width of \(X(3872)\)  as a function of its mass within one sigma range in Fig. REF .
We can see that there is no zero decay width when \(X(3872)\)  under \(D^0D^{0*}\)  threshold as \(D^{0*}\)  can be off shell. When the \(D^0 D^{0*}\)  threshold opens, the decay width of \(X(3872)\)  increases rapidly.
Finally, the decay width of \(X(3872)\)  is predicted to be \(\Gamma [X(3872)]\simeq 2 \)  MeV
when we take the world average mass \(m_{X(3872)} = 3871.69\)  MeV from the PDG [2]}.
This result is consistent with the measured widths in experiments [4]}, [5]}.
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